The present invention relates to a data transmission device, a data receiving device, a data transmitting method, and a data receiving method, which can be used for digital satellite broadcasts and the like capable of multiplex transmission of, for example, program broadcasting and data broadcasting.
A satellite broadcast is a broadcast that uses an artificial satellite in an orbit around the earth keeping 36000 km above the earth. The satellite broadcast uses broadcasting satellites (BS), or communications satellites (CS). Both of the satellite broadcasts can be received using simple receiving facilities. Concerning such satellite broadcasts, the same transmitted wave from one transmission point, that is to say, a stationary orbit position, can cover all over the country. Because the satellite broadcasts can achieve a nationwide broadcast economically and efficiently, the satellite broadcasts provide nationwide popularization more easily than terrestrial broadcasting businesses, and at the same time provide a solution to a blind-spot problem. In Japan, as shown in FIG. 19, the one transmission point comprises seven transponders having a pair of channels. As channels currently being used, channels 5 and 7 are used for WOWOW and NHK1 respectively; and channels 9 and 11 are used for Hi-vision and NHK2 respectively.
In the BS broadcast like this, as shown in FIG. 20, MPEG-TS (MPEG Transport Stream) is generated. The MPEG-TS is a multiplexed data stream that is converted from a data stream including video and audio data at a coding bit rate corresponding to a given transmission rate in a given broadcasting band. According to this MPEG-TS, the multiplexed data stream is transmitted in the following order: video data V1, audio data A1, data D1, video data V2, audio data A2, data D2, . . . .
However, in the satellite broadcasts as described above, if a plurality of broadcasting programs having different transmission rates are multiplexed and transmitted, there occurs a problem that the maximum transmission rate is not utilized effectively.
On the other hand, if the broadcasting programs are transmitted at the maximum transmission rate, another problem arises: when multiplexing and transmitting various kinds of data as described above at random ratios, some data may not be visualized in real time because units of the data required for visualization on a receiving side cannot be transmitted in a block.